The stress corrosion cracking of 18% Ni maraging steel has been investigated in 0.6 N sodium chloride solutions. The principal aim was to determine the dependence of the cracking process on structural and environmental variables. The susceptibility towards intergranular stress corrosion cracking was found to be associated with the state of the prior austenite grain boundary network. Processing variables which produce changes in the size or chemical nature of the grain boundaries were found to have the greatest effect on susceptibility. The cracking propensity was found to be effected by solution pH and the process appeared to be under cathodic control. Crack initiation was associated with the formation of structurally independent surface fissures, whose growth depend on the solution condition rather than the pH value. Investigations were carried out into the environmental conditions required to produce stress corrosion and hydrogen embrittlement failures. The evidence produced indicates that these two mechanisms can be characterised by the potential range under which they occur and by the associated fracture surfaces. As a result the failures obtained for Maraging Steels in 0.6 N sodium chloride solutions under naturally corroding conditions, can be considered to be due to a stress corrosion cracking mechanism.